Studies on Fracton in Silica Aerogels by Ramman Scattering

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In 1990 fiscal year, Ramman scattering and neutron inelastic scattering experiments were performed. The results are reported in Phys. Rev. Letters and is summarized as follows. Two samples were prepared in PH7 solvent(N-sample)and in PH8.5 solvent(B-sample). Compared Ramman scattering result with neutron scattering result, we found that there exist two types of fracton. One is scaler fracton observed above crossover frequency nu e=10GHz and the another is vector fraction observed below nu e. In N-sample, fracton dimension of scaler fracton d^^=_s and that of vector fraction d^^=_b are determined to be 1.3 and 2.2, respectively. In B-sample, d^^=_s=0.9 and d^^=_b=1.7. Here fracton dimension is a physical quantity characterizinle, dynamic behavior of fracton. Results show that fractal dimension depends on PH and is not the universal physical quantity. Relation d^^=_s<d^^=_b is, however, hold both in N- and B-sample.In 1991 fiscal year, four samples x-7ere prepared in PH 7.03 7.5, 8.0 and 8.5 solvents. The purpose is to obtain a detailed information about the dependence of fracton on PH. Thouch Ramman scattering experiment was made, the very strong elastic scattering prevented us to observe fracton. This comes from poor contrast of 5 path interferometer(Burleigh RC-110)used in Hokkaido University. Until we introduce the 3+3 path tandem interferometer(contrast is about 10^<15>)we put off Ramman scattering experiment. Brillouin scattering experiment in beta-BiNbO_4 was performed instead. The elastic constants were determined in cylindrical sample alona a^* axis of beta-BiNbO_4. This result was reported at annual meeting of Physical Society of Japan in 1992.